Step 1 Lactose enters

I End products 1 Enzymes that break down lactose

Analysis and Conclusions

1. What substance serves as an inducer in the lac operon?

2. How might a mutation in the regulator gene affect the lac operon?

3. Look at the diagram you made in step 12. Refer to your diagram, and predict what will happen when the inducer is no longer present.

4. How would the loss of the promoter site from the operon affect the production of the enzymes needed to utilize lactose?

5. In homes and apartments, a consistent temperature is maintained by means of a thermostat, which regulates when heating (or air conditioning) is turned on or off. In what way does the lac operon function like a thermostat?

6. Biological processes often take place in a series of sequential steps called a biochemical pathway. Many biochemical pathways are controlled by feedback inhibition. In feedback inhibition, a pathway's end product affects an earlier step in the pathway and causes the pathway to stop. Explain how the function of the lac operon is similar to the process of feedback inhibition.

Further Inquiry

1. Use classroom or library references to find examples of feedback inhibition in biology. Describe why models of feedback inhibition are sometimes called feedback loops.

2. The products of the lac operon are produced when lactose is present. In this way, the presence of a specific molecule stimulates transcription of the structural genes. In contrast, some operons are repressed when a specific molecule is present. Use classroom or library references to find out how the trp operon functions in E. coli. Then, compare the function of the trp operon with the function of the lac operon.

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